In the ALD method that is one of thin-film forming techniques, two kinds of gases composed mostly of elements constituting a film to be formed are alternately supplied onto a deposition target substrate, and formation of a thin film in one or a few atomic layers is repeated plural times on the substrate, thereby forming a film having a desired thickness. For example, a source gas containing Si and an oxidizing gas containing O are used when a SiO2 film is formed on the substrate. A nitrizing gas is used instead of the oxidizing gas when a nitride film is formed on the substrate.
In the ALD method, while the source gas is supplied, the source gas only for one or a few layers is adsorbed into a substrate surface, and the excess source gas does not contribute to the deposition. This is well known as deposition self-stopping action (self-limiting function).
The ALD method advantageously has both high step coverage and film-thickness controllability compared with a generally used CVD (Chemical Vapor Deposition) method, so that the ALD method is expected to be practically applied to formation of a capacitor of a memory element or an insulating film called “high-k gate”. Further, since the insulating film can be formed at a low temperature of about 300° C. in the ALD method, the ALD method is also expected to be applied to formation of a gate insulator of a thin-film transistor in a display device such as a liquid crystal display in which a glass substrate is used.
A conventional ALD apparatus will be described below.
FIG. 4 is a schematic diagram illustrating an example of a conventional ALD apparatus. Referring to FIG. 4, an ALD apparatus 70 includes a deposition container (deposition chamber) 12, a gas supply unit 14, and an exhaust unit 16.
The deposition container 12 is formed in a metallic hollow box shape and grounded. In the deposition container 12, an antenna array 28 including plural antenna elements 26 and a substrate stage 32 embedded with a heater 30 are sequentially provided from an upper wall side toward a lower wall side. In the antenna array 28, a virtual plane (array direction) that is formed by the plural antenna elements 26 disposed in parallel to each other at predetermined intervals is provided in parallel with the substrate stage 32.
As illustrated in FIG. 5 that is of a plan view, the antenna element 26 is a rod-shaped monopole antenna (antenna body) 39 made of a conductive material having a length of (2 n+1)/4 times (n is 0 or a positive integer) a wavelength of high-frequency power, and the antenna element 26 is accommodated in a cylindrical member 40 made of a dielectric material. The high-frequency power generated by a high-frequency power supply unit 34 is distributed by a distributor 36 and supplied to each antenna element 26 through an impedance matching box 38, thereby generating plasma around the antenna element 26.
Each antenna element 26 is disclosed in Japanese Patent Publication Laid-Open No. 2003-86581 proposed by the applicant. Specifically, the antenna element 26 is mounted to a lateral wall of the deposition container 12 while electrically insulated so as to be extended in a direction orthogonal to a gas flow direction of the oxidizing gas supplied toward a substrate stage 32 from a supply hole 20b. The antenna elements 26 are disposed in parallel to each other at predetermined intervals, and the antenna elements 26 are disposed adjacent to each other such that power feeding positions of the antenna elements 26 are located on lateral walls which are on the opposite side from each other.
An operation during the deposition of the ALD apparatus 70 will be described below.
During the deposition, a substrate 42 is placed on an upper surface of the substrate stage 32. The substrate stage 32 is heated with the heater 30, and the substrate 42 placed on the substrate stage 32 is maintained at a predetermined temperature until the deposition is ended.
Specifically, when a SiO2 film is formed on the substrate surface, after the deposition container 12 is horizontally evacuated with the exhaust unit 16, the source gas containing a Si component is horizontally supplied from the gas supply unit 14 into the deposition container 12 through a supply pipe 18a and a supply hole 20a formed in a left wall of the deposition container 12. Therefore, the source gas is supplied to the surface of the substrate 42 and adsorbed. During this process, the plasma is not generated by the antenna element 26.
Next, the supply of the source gas is stopped, and the excess source gas other than source gas adsorbed into the surface of the substrate 42 is horizontally exhausted from the deposition container 12 through an exhaust hole 24 formed in a right wall of the deposition container 12 and an exhaust pipe 22 with the exhaust unit 16.
Subsequently, the oxidizing gas is horizontally supplied from the gas supply unit 14 into the deposition container 12 through a supply pipe 18b and the supply hole 20b formed in the left wall of the deposition container 12. Simultaneously, the high-frequency power is supplied from the high-frequency power supply unit 34 to each antenna elements 26. Therefore, the plasma is generated around each antenna element 26 using the oxidizing gas, and the source gas adsorbed into the surface of the substrate 42 is oxidized.
Then, the supply of the oxidizing gas and the supply of the high-frequency power to the antenna element 26 are stopped, and the excess oxidizing gas that does not contribute to the oxidation and the reaction product are horizontally exhausted through the exhaust hole 24 formed in the right wall of the deposition container 12 and the exhaust pipe 22 with the exhaust unit 16.
Thus, the SiO2 film is formed in one or a few atomic layers on the substrate 42 through a series of processes including the supply of the source gas→the exhaust of the excess source gas→the supply of the oxidizing gas→the exhaust of the excess oxidizing gas. The SiO2 film having a predetermined thickness is formed by repeating the series of processes several times.
Japanese Patent Publication Laid-Open Nos. 2006-310813, 2007-473824, and 2002-280378 can be cited as examples of the prior art document related to the invention.
Japanese Patent Publication Laid-Open No. 2006-310813 proposed by the applicant is a single wafer-type ALD apparatus in which a monopole antenna is disposed as the plasma source in the deposition container. Japanese Patent Publication Laid-Open No. 2007-473824 is a single wafer-type ALD apparatus aimed at a semiconductor wafer, and a shower head and a substrate heater are used as a parallel plate type device. Japanese Patent Publication Laid-Open No. 2002-280378 is a batch-type ALD apparatus aimed at the semiconductor wafer, and a remote plasma method is adopted using parallel electrode.